1. Field of the Invention
The present invention relates to a deflection yoke attached to an inline type color cathode-ray tube and a mis-convergence correction method for a color cathode-ray tube correcting mis-convergence on the Y-axis of a screen. The present invention particularly relates to a deflection yoke and a mis-convergence correction method capable of simultaneously correcting comatic aberration and mis-convergence.
2. Description of the Related Art
There exists a color display device provided with an inline type color cathode-ray tube (to be referred to as xe2x80x9ccolor CRTxe2x80x9d hereinafter). In the inline type color CRT, electron beams are produced in a vacuum valve from electron guns for blue, green, and red, respectively. The electron beams are deflected in X and Y-axes directions by a deflection yoke made up of an electromagnetic coil and the like and reach a phosphor film through a shadow mask.
In the inline type color CRT stated above, electron beams pass into a heavily distorted deflecting magnetic field at the time of deflecting the electron beams in the X and Y-axes directions by means of the deflection yoke. Due to this, three electron beams disadvantageously, poorly converge. This phenomenon is called mis-convergence.
To solve the disadvantage, there is provided a color CRT which adopts a system called inline self-convergence system. FIGS. 1A and 1B are typical views showing the inline self-convergence system. In the inline self convergence system, a deflecting magnetic field 101 (FIG. 1A) having a pin cushion type, horizontally deflecting magnetic field distribution, and a deflecting magnetic field 102 (FIG. 2B) having a barrel type, vertically deflecting magnetic field distribution are formed. Three electron beams 10B, 10G and 10R emitted from three inline electron guns aligned in the same horizontal plane are deflected by these deflecting magnetic fields 101 and 102 and converge at arbitrary points on a screen, respectively.
The inline self-convergence system has advantages in that it suffices to provide a small number of electrical circuits, adjustment is required infrequently and the like to converge the three electron beams 10B, 10G and 10R and in that the highly accurate convergence can be realized.
Nevertheless, a focus voltage Vfh capable of minimizing a horizontal diameter of a spot and a focus voltage Vfv capable of minimizing a vertical diameter of a spot differ from each other and the difference between the both focus voltages xcex94Vf=Vfhxe2x88x92Vfv is negative. Namely, the convergence state of the electron beams in the vertical direction is an over-focus state. For that reason, if the distortions of the shapes of the electron beams on the periphery of the screen are finely observed, it is found that halos occur in vertical direction because of astigmatism. FIG. 2 is a typical view showing electron beam spots on a conventional screen. Electron beams 10B, 10G and 10R are influenced by the magnetic field distortions of the self convergence deflecting magnetic fields 101 and 102 when passing into the fields 101 and 102. As a result, the shapes of the electron beam spots become round at the center of the screen, which is free from deflection. However, if the electron beams are deflected to the peripheral portions of the screen, the shape of each electron beam spot becomes one having an oblong beam core 111 and a radial halo 112 generated above and below the beam core 111, i.e., a distorted shape. The diameter of each of the distorted electron beam spots on the peripheral portions of the screen is, therefore, larger than that of the completely round spot at the center of the screen, with the result that resolution on the peripheral portions of the screen considerably deteriorates.
Further, because of the asymmetry of deflecting magnetic fields, comatic aberration, which causes mis-convergence occurring between the center beam (G) and the side beams (B, R) among the three electron beams as deflection frequency is higher. It is, therefore, necessary to eliminate the comatic aberration, as well. FIGS. 3A to 3D are typical views showing mis-convergence. FIG. 4 is a typical view showing one example of a lateral raster distortion. The mis-convergence caused by the comatic aberration includes an arc distortion, as shown in FIG. 3A, in which a red line 20R and a blue line 20B separate from each other in lateral direction on the upper and lower ends of the screen, a distortion, as shown in FIG. 3B, in which a red line 21R and a blue line 21G separate from each other in longitudinal direction on the upper and lower ends of the screen, and a distortion, as shown in FIG. 3C, in which a red line 21R and a blue line 21B separate from a green line 21G in longitudinal direction. Further, as shown in FIG. 3D, if a figure which should be originally a rectangle is distorted into a trapezoid 30 due to the influence of a pin cushion type magnetic field distribution and a barrel type magnetic field distribution, the distorted figure is visually inappropriate particularly for CAD, CAM or the like and causes much deficiency. Moreover, as shown in FIG. 4, if there is a parallel distortion in which a red line 21R and a blue line 21B are deviated from a green line 21G in the lateral direction of the screen, a resultant image is difficult to view.
The mis-convergence stated above is normally considered to derive from the deviation between the mechanical center of three electron beams and that of a deflecting magnetic field from the viewpoint of the electron guns of a color CRT. Further, the mis-convergence is considered to derive from a design in which a variable resistor for deflecting current control provided on a deflection coil simultaneously corrects comatic aberration and the distortion of an image from the viewpoint of a deflection yoke.
To solve the above-stated disadvantages, there has been conventionally proposed a mis-convergence correction method using a deflection yoke provided with a pair of E-shaped magnetic members (Japanese Patent Application Laid-Open No. 9-17355). FIG. 5 is a typical view showing a conventional deflection device disclosed by Japanese Patent Application Laid-Open No. 9-17355. FIG. 6 is a typical view showing magnetic fields generated by the conventional deflection device.
This conventional deflection device has a pair of E-shaped magnetic members 41 and 42 provided on a deflection yoke bobbin attached to the neck portion 40 of a color CRT. Coma correction coils 51a and 51c are wound around the leg portions 41a and 41c of the E-shaped magnetic member 41 on both ends thereof, respectively. A coma correction coil 51b is wound around the central leg portion 41b of the E-shaped magnetic member 41. Likewise, coma correction coils 52a and 52c are wound around the leg portions 42a and 42c of the E-shaped magnetic member 42 on the both ends thereof, respectively. A coma correction coil 52b is wound around the central leg portion 42b of the E-shaped magnetic member 42.
In the conventional deflection device constituted as stated above, a pin cushion type deflecting magnetic field 60a is generated between the leg portions 41a and 42a, and a pin cushion type deflecting magnetic field 60c is generated between the leg portions 41c and 42c as shown in FIG. 6. A barrel type deflecting magnetic field 61b is generated between the leg portions 41b and 42b. As a result, astigmatism and mis-convergence can be simultaneously corrected.
Although the conventional mis-convergence correction method stated above has an advantage in that astigmatism and mis-convergence can be simultaneously corrected by simple means relatively easily, the following disadvantages are still to be solved.
Since three coma correction coils are provided for each E-shaped magnetic member, the mold structure of a supporter for an E-shaped magnetic member becomes complicated. Consequently, production cost is increased and it is economically difficult to work this method.
Furthermore, as shown in FIG. 4, while the horizontal deviation between the red line 21R and the blue line 21B, and the green line 21G on the upper and lower ends of the screen are small, the vertical deviation between the red line 21R and the blue line 21B, and the green line 21G on the left and right ends of the screen is large. For that reason, there is a fundamental limit to correcting deviations.
Moreover, as shown in, for example, Japanese Patent Application Laid-Open No. 11-40079, an E-shaped magnetic member is to be arranged on the electron gun-side rear end portion of a deflection yoke. FIG. 7 is a typical view showing how the E-shaped magnetic member is disposed. FIG. 8 is a typical view showing mis-convergence resulting from asymmetry of magnetic flux densities. The arrangement shown therein is undesirable from the viewpoint of the structure of the deflection yoke for the following reasons. As shown in FIG. 7, a low hysteresis, high permeable magnetic member 74 is normally attached to a bobbin 73 while intersecting a leakage magnetic flux from a horizontal deflection coil 72 on the rear end portion of the deflection yoke 70 on an electron gun 71 side. This is intended to correct mis-convergence generated because the magnetic flux distribution densities of lines 22G, 22B and 22R become asymmetric on the left and right positions of a screen as shown in FIG. 8. In case of employing the E-shaped magnetic member, therefore, such a mis-convergence correction method cannot be adopted.
In these circumstances, a mis-convergence correction method other than a method of providing a coma correction coil on an E-shaped magnetic body is desired.
It is, therefore, an object of the present invention to provide a deflection yoke and a mis-convergence correction method for a color cathode-ray tube which can be manufactured at low cost and which can ensure the correction of both astigmatism and mis-convergence.
According to one aspect of the present invention, a deflection yoke for inline type color cathode-ray tube with a valve accommodating three electron guns and having a neck portion and a funnel portion comprises a vertical defection coil which defects beams emitted from the three electron guns in a vertical direction of a screen, auxiliary coils connected in series to the vertical deflection coil, and a U-shaped magnetic member having leg portions and being arranged such that the leg portions face the neck portion of the valve. The auxiliary coils are wound around each of the leg portions of the U-shaped magnetic member.
In the present invention, the auxiliary coils wound around the U-shaped magnetic member are connected to the vertical deflection coil in series. Therefore, a quadruple magnetic field lens function resulting from a type of quadruple coils is generated. As a result, a pin cushion distortion in the vertical direction of a screen can be corrected and mis-convergence can be corrected, as well.
According to another aspect of the present invention, a mis-convergence correction method for a color cathode-ray tube provided with the above-described deflection yoke, the method comprises the step of adjusting each of inductances of the auxiliary coils.